Juvenile Fasciola hepatica at different stages of development were isolated from the liver parenchyma of experimentally infected rats. Their energy metabolism was studied by incubation with D-[16-14C]glucose and compared with that of juveniles isolated immediately after in vitro emergence from the metacercarial cysts. These studies confirmed that freshly excysted juveniles ... read more have an aerobic energy metabolism, but are already fully equipped for life in the absence of oxygen. A functioning Krebs cycle was a true characteristic of all parenchymal stages of F. hepatica, but its capacity slowly decreased during development. Concomitantly, acetate became the major end product. This formation of acetate was an aerobic process and it was the most important source of energy for the exponentially growing fluke after twelve days of development. It might, therefore, be an important new target for anthelmintics. The decrease in Krebs cycle activity was not caused by a lack of oxygen nor by a decreased capacity of the respiratory chain. The freshly excysted juvenile had endogenous glycogen stores which were degraded during fasting and replenished in the presence of glucose. show less